There are two kinds of frame structures in a Long Term Evolution (LTE) system. The frame structure Type 1 is applicable to full-duplex Frequency Division Duplexing (FDD) and half-duplex FDD. A radio frame has a length of 10 ms, and is composed of 20 time slots, each of which has a length of 0.5 ms and which are numbered from 0 to 19 respectively. FIG. 1 is a schematic diagram of a frame structure of an FDD mode. As shown in FIG. 1, one subframe is composed of two consecutive time slots. For example, the subframe i is composed of two consecutive time slots 2i and 2i+1. Regardless of the half-duplex FDD or the full-duplex FDD, both of uplink and downlink are transmitted at different frequencies. However, in half-duplex FDD, a User Equipment (UE) cannot transmit and receive data at the same time, whereas in full-duplex FDD, there is no restriction to this, i.e., for a UE, data can be received on 10 downlink subframes and transmitted on 10 uplink subframes at the same time in an interval of every 10 ms.
The frame structure Type 2 is applicable to Time Division Duplexing (TDD). FIG. 2 is a schematic diagram of a frame structure of a TDD mode. As shown in FIG. 2, one radio frame has a length of 10 ms, and is composed of two half frames having a length of 5 ms. One half frame is composed of 5 subframes having a length of 1 ms. Supported uplink-downlink configuration is as shown in Table 1. In the table, “D” denotes that the subframe is a downlink subframe, “U” denotes that the subframe is an uplink subframe, and “S” denotes that the subframe is a special subframe. Each special subframe is composed of a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS), and has a total length of 1 ms. Each subframe i is composed of two time slots 2i and 2i+1 each having a length of 0.5 ms. The frame structure Type 2 supports 5 ms downlink-to-uplink switch-point periodicity and 10 ms downlink-to-uplink switch-point periodicity. In the 5 ms downlink-to-uplink switch-point periodicity, the special subframe exists in both half frames. In the 10 ms downlink-to-uplink switch-point periodicity, the special subframe exists in the first half frame only. Subframes 0 and 5 and the DwPTS are always reserved for downlink transmission. The UpPTS and the subframe immediately following the special subframe are always reserved for uplink transmission. Therefore, for the 5 ms downlink-to-uplink switch-point periodicity, the UpPTSs and subframes 2 and 7 are reserved for uplink transmission; for the 10 ms downlink-to-uplink switch-point periodicity, the UpPTS and the subframe 2 are reserved for uplink transmission.
TABLE 1Uplink-downlink configurationUplink-downlinkDownlink-to-uplinkSubframe numberconfigurationswitch-point periodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
In the LTE, three kinds of downlink physical control channels are defined as follows: a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid Automatic Retransmission Request Indicator Channel (PHICH), and a Physical Downlink Control Channel (PDCCH).
Information borne by the PCFICH is used to indicate the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols transmitted in the PDCCH in a subframe, and is transmitted on the first OFDM symbol in the subframe, and a frequency position of the information is determined by a downlink bandwidth of a system and a cell Identity (ID).
The PHICH is configured to bear Acknowledgement/Negative Acknowledgement (ACK/NACK) feedback information of uplink transmission data. The number and time-frequency position of the PHICH may be determined by a system message and a cell ID in a Physical Broadcast Channel (PBCH) of a downlink carrier where the PHICH is located.
The PDCCH is configured to bear Downlink Control Information (DCI), including scheduling information of a Physical Uplink Shared Channel (PUSCH), scheduling information of a Physical Downlink Shared Channel (PDSCH) and uplink power control information.
For FDD, when a UE detects, in the subframe n, the PDCCH channel which belongs to the UE and bears the scheduling information of the PUSCH, or when the UE receives, in the subframe n, the PHICH which belongs to the UE and corresponds to the PUSCH, the UE will transmit in the subframe n+4 data of the PUSCH depending on circumstances.
For the uplink-downlink configurations 1 to 6 for TDD, when the UE detects, in the subframe n, the PDCCH channel which belongs to the UE and bears the scheduling information of the PUSCH, or when the UE receives, in the subframe n, the PHICH which belongs to the UE and corresponds to the PUSCH, the UE will transmit in the subframe n+k data of the PUSCH depending on circumstances. For the uplink-downlink configuration 0 for TDD, when the UE detects, in the subframe n, the PDCCH channel which belongs to the UE and bears the scheduling information of the PUSCH and UL Index signalling in the scheduling information has an upper bit of 1, or when the UE receives, in the subframe 0 and the subframe 5, the PHICH which belongs to the UE and corresponds to the PUSCH and the IPHICH is equal to 0, the UE will transmit in the subframe n+k data of the PUSCH depending on circumstances. When the UE detects, in the subframe n, the PDCCH channel which belongs to the UE and bears the scheduling information of the PUSCH and UL Index signalling in the scheduling information has a lower bit of 1, or when the UE receives, in the subframe 0 and the subframe 5, the PHICH which belongs to the UE and corresponds to the PUSCH and the IPHICH is equal to 1, the UE will transmit in the subframe n+7 data of the PUSCH depending on circumstances. The value of k hereinbefore is as shown in Table 2:
TABLE 2Diagram of the value of k for configurations 0-6 for TDDUplink-downlinkconfigurationsDownlink subframe number nfor TDD01234567890464616464244344444454677775
In the Release (R) 8/9 of the LTE system, a Common Reference Signal (CRS) is designed to measure the channel quality and demodulate received data symbols. The UE may measure the channel through the CRS, so as to support the UE to reselect a cell and switch to a target cell, and to measure the channel quality in a UE connection state. In LTE R10, in order to further improve the average spectrum efficiency of the cell and the cell-edge spectrum efficiency as well as the throughput of each UE, two reference signals are defined respectively: a Channel State Information Reference Signal (CSI-RS) and a Demodulation Reference Signal (DMRS). Status information of a channel is acquired by the CSI-RS. A Precoding Matrix Index (PMI), a Channel Quality Indicator (CQI) and a Rank Indicator (RI), which the UE needs to feed back to an eNB, may be calculated by measuring the CSI-RS. Data borne on a downlink shared channel is demodulated by the DMRS. By DMRS demodulation, the interference between different receiving sides and between different cells may be reduced by a beam method, the performance degradation caused by codebook granularity may be reduced, and the overhead of the downlink control signalling is reduced to a certain extent.
In LTE R8, R9 and R10, the PDCCH is mainly distributed at first 1, 2 or 3 OFDMs of one subframe. The specific distribution needs to be configured according to different subframe types and the number of CRS ports, as shown in Table 3:
TABLE 3The number of PDCCHThe number of PDCCHSubframeOFDM symbols of NRBDL > 10OFDM symbols of NRBDL ≦ 10Subframe 1 and subframe 61, 22in subframe Type 2Subframe supporting a1, 22Multicast Broadcast SingleFrequency Network(MBSFN) on a carrier of thePDSCH, the CRS isconfigured for port 1 or 2Subframe supporting the22MBSFN on the carrier of thePDSCH, the CRS isconfigured for port 4Subframe not supporting a00carrier transmitted on thePDSCHNon-MBSFN subframe1, 2, 32, 3configured as a PRS(except the subframe 6 ofthe subframe structure Type2)All other things1, 2, 32, 3, 4
Blind detection is required at each receiving side according to the first three symbols. The initial position of the blind detection is related to the number of elements of the control channel, radio network temporary identity allocated to the receiving side and different control information. The control information may generally be classified into common control information and dedicated control information. The common control information is generally placed in common search space of the PDCCH, and the dedicated control information may be placed in all common space and the dedicated search space. The receiving side determines, after the blink detection, whether there is a common system message, downlink scheduling information or uplink scheduling information in the current subframe. Since the downlink control information has no Hybrid Automatic Retransmission Request (HARQ) feedback, it is necessary to ensure that an error rate of detection is as low as possible.
In order to obtain a greater operating spectrum and system bandwidth, several consecutive component carriers (spectrums) distributed on different frequency bands may be aggregated by carrier aggregation technology to form a bandwidth that may be used by LTE-Advanced, e.g., 100 MHz. That is, the aggregated spectrums are divided into n component carriers (spectrums), and the spectrums in each component carrier (spectrum) are consecutive. The spectrum is divided into a Primary Component Carrier (PCC) and a Secondary Component Carrier (SCC), which are also referred to as a primary cell and a secondary cell.
Over an LTE R10 heterogeneous network, since there is stronger interference between different types of base stations, in consideration of the interference of a Macro eNodeB with a Pico eNodeB and the interference of a Home eNodeB with the Macro eNodeB, a resource muting method is proposed to solve mutual interference between different base stations. The specific resource muting method may be a subframe-based muting method (e.g., an Almost Blank Subframe (ABS) method), and may also be a resource-element-based method (e.g., a CRS muting method).
However, the methods above not only increase resource waste, but also bring about severe restriction to scheduling. In particular, when the ABS configuration of the Macro eNodeB is considered, if there are many deployed Pico eNodeBs, there are more ABSs which need to be configured by the Macro eNodeB, which will have greater impact on the Macro eNodeB, thereby increasing the resource waste and further increasing the scheduling delay. Moreover, it is impossible to solve the interference between CRS resource and data resource, and it is also impossible for the muting CRS method to solve the interference between data resources. Additionally, the methods above have bad backward compatibility, so more standardization efforts may be required while the access delay is increased.
At the LTE R11 stage, it is possible to introduce more UEs to perform transmitting on the MBSFN subframe, which will result in that the capacity of two OFDM symbols of the PDCCH used for bearing is not enough. In order to ensure the backward compatibility to R8/R9/R10 UEs, new resources used for transmitting the control information needs to be developed on the PDSCH resource, and Coordinated Multi-Point Transmission (COMP) technology is introduced at the R11 stage. Such technology may solve the interference between difference types of cells in a way of space division, and save the overhead of resources, thereby avoiding the resource waste caused by muting and reducing the restriction to scheduling. However, the existing manner for the time-domain PDCCH cannot solve the problem in the way of space division, and in consideration of the backward compatibility to the R8 and R9, a manner for such a control channel as the time-domain PDCCH must be reserved. Therefore, how to solve the interference between the control channels by space division technology is needed to be meticulously studied.